The present invention relates to a rain sensor having two spaced conductive paths lying parallel to each other and arranged on the windshield of a motor vehicle, there being an evaluation electronics system connected to the two conductive paths.
It is known to arrange rain sensors on the windshield of a car in the region of the windshield wiper. As a function of the amount of wetness present on the windshield, these rain sensors provide to an evaluation circuit within the motor vehicle a signal which is used ordinarily to control the windshield wiper.
Sensors which are located on the outside of the windshield consist of two conductive paths, not in contact with each other, which have conductive-path sections which are parallel to each other and which engage in comb-like manner in each other but are not electrically connected to each other. They are developed as structures of constant width. The conductive paths are provided with electric connecting devices. During a rain storm the electrically conductive paths are bridged by drops of water with resulting electric characteristics describable by an electric measuring graph.
A short-circuiting of the conductive paths by the drops of water effects a change in the total resistance of the sensor. As a function of the degree of wetness on the windshield at the time, a reproducible electric signal can thus be produced via the change in resistance.
In order to obtain a specific resistance, the conductive paths of the rain sensor must have a given length. This gives the result that the rain sensor takes up a certain amount of space on the windshield.
In particular, with the rain sensor arranged on the windshield, a sensor of large size interferes with the field of view of the driver. In order to reduce this disadvantage the rain sensor is generally so arranged that it is covered by the rear-view mirror present within the vehicle.